Help Needed With My Ipod Classic 120GB

Hello People. I will try an make this as short and sweet as i can...I have a problem with my 120GB classic and that is i can transfer songs onto it fine but then when i transfer a film over that i have converted to the iPod formats the film doesn't play so when i reconnect the iPod back to iTunes to delete the film it not only deletes the film it deletes all my songs to and iTunes will start to freeze and the only way around the freezing is if i un-install iTunes and then connect the iPod to my computer and do a Quick Format. The same things happens if i do it the other way round if i have no songs on the iPod i can transfer a film no problem and it plays but once i start to transfer songs on half way through the syncing process the syncing picture on my iPod will disappear but it still says its syncing at a snails passe on iTunes and then when it has finished syncing and i check the iPod the songs and the film i have transferred have been deleted. Also when i try and restore the iPod without doing a quick format the error message comes up saying cannot restore error message 1415 and something about the folders i'm looking for cannot be found..... apologies for the essay i have wrote any help of you people would be much appreciated